Chronic Dev Team has updated GreenPois0n to RC6.1 which incorporates fix by Comex for iBooks DRM error after jailbreaking iPhone, iPad or iPod touch on iOS 4.2.1 it with GreenPois0n RC5/6.

As we covered it earlier, Apple’s iBooks app refuses to open digital books loaded with DRM if the device is jailbroken on 4.2.1. Comex discovered that the app was checking if the operating system allowed it to execute an unsigned binary, and if it did, the book wouldn’t open. Now both PwnageTool 4.2 and Sn0wbreeze 2.2 already includes this fix. If you are jailbroken with Redsn0w 0.9.6 or 0.9.7, you can simply use “iBooks Fix” app from Cydia, or just run this latest version of GreenPois0n RC6.1 over your existing RC5 or RC6 jailbreak. No restore is required.

Once you are done, all your DRM-filled books should once again be accessible right from the iBooks app on your jailbroken iOS device.